German Patent Specification No. 1,129,894 describes a process for sealing or consolidating geological formations against water or gas by means of polyurethane, wherein reaction components forming a cross-linked product with the group --NH--CO--O--, namely a di- or polyisocyanate and a polyol comprising at least three reactive OH groups, mixed together in a liquid vehicle, are forced under pressure into the formation to be sealed or consolidated.
In forming the polyurethane, polyols are usually used having an average molecular weight of 400-600 and an OH number of 350-400. These polyols may be replaced up to about 15% or even completely by a plasticizer, in particular castor oil. Dispite many disadvantageous properties, castor oil is used in practice as a sole or partial cross-linking agent for isocyanates for consolidating geological formations, see for example "Gluckauf" 104 (1968) Volume 15, pages 666-670, German Patent Specification DOS 2,123,271, DBP 1,758,185, and DBP 1,784,458.
One disadvantage of high castor oil contents is the insufficient flexibility which it gives to the hardening polyurethane, which may lead to a premature destruction of the consolidated state of the geological formation, especially with the high dynamic stress on coal and the surrounding rock occurring in mechanical coal production processes in open-cast mining. As the proportion of castor oil in the polyol component is raised, the modulus of elasticity, the compression strength and the bending strength of the polyurethane which brings about the consolidation of the geological formation are reduced, so that the rock pressure and the action of external forces connected with the mechanical production process may cause slip of the consolidated formations.
A further disadvantage is the relatively high viscosity of castor oil, which is approximately 1000 mPa s at 25.degree. C. With higher contents of castor oil in the polyol component, the viscosity of the entire system is raised to such a value that troublefree penetration into the smallest cracks and crevices and the complete wetting of the surface are no longer guaranteed.
The immiscibility of castor oil with water is also a disadvantage. If damp or wet rock is to be consolidated, the castor oil may be separated from the system by the water absorption of the polyol compounds, which are very miscible with water, and thus the castor oil no longer reaches the diisocyanate for reaction. Indeed, a known method for determining castor oil in polyol compounds consists of separating the castor oil by displacement with water.
Another disadvantage is that the castor oil reduces the binding force between the polyurethane and the rock or coal at high castor oil contents in the polyol. Thus, the structure of the consolidated formations is weakened.